1. Field of the Invention
The present invention relates to a power supply circuit for generating an internal power supply voltage from one or more power supplies.
2. Description of the Related Art
Proposed in a conventional practice is a power supply management circuit that controls the operation of an electronic device by either a voltage supplied from an external power supply or a voltage from a battery. This power supply management circuit includes a voltage comparator circuit for comparing the voltage from the external power supply with the voltage from the battery, and a selection circuit for selecting either one of the voltages in response to an output signal of the voltage comparator circuit.
Since the power supply management circuit in the above-described conventional practice includes the voltage comparator circuit, the circuitry configuration thereof is complicated and the circuit scale thereof is large. Where the power supply management circuit (hereinafter referred to as “power supply circuit”) is incorporated into a mobile electronic device, an increase in the circuit scale is undesirable in the light of a demand for reduced size of the electronic devices.
Also, when the power supply circuit generates the internal power supply voltage from more than a single power supply circuit, a drop in power supply voltage supplied therefrom is undesirable and it is desired that the power supply voltage be maintained as long as possible.